1. Field of the Invention
The present invention relates to thixotropic compositions comprising leather fibers as a thixotropic agent and to a method for rendering compositions thixotropic.
2. Description of the Prior Art
The desirability of thickening liquids for use in certain applications has been recognized in the prior art and it has been proposed to thicken a variety of liquids by incorporating therein inert inorganic materials such as mica, diatomaceous earth, talc, alumina, graphite, and the like, and, in particular, silica aerogels and asbestos have been used to achieve a thixotropic effect.
For example, U.S. Pat. No. 2,260,625 Kistler proposes to thicken oily liquids such as lubricating oils to convert the same into greases by adding a silica aerogel.
U.S. Pat. No. 2,892,730 Kloepfer et al proposes thickening organic liquids containing high molecular weight film formers with oxides of silicon, aluminum and titanium.
U.S. Pat. No. 2,610,960 Nordlander proposes rendering polymerizable organic liquids thixotropic by incorporating vermiculite.
U.S. Pat. No. 2,887,461 Horst proposes rendering laminating compositions thixotropic by adding silica aerogels.
One objective of many of the above patents is to overcome the problem of drainage of composition away from coated or filled objects or articles to which the composition has been applied.
U.S. Pat. No. 3,525,689 Marotta discloses a number of prior art references dealing with thixotropic compositions; the specific concept of Marotta involves using the combination of a specified silica material and chrysotile asbestos.
Other references dealing with thickened or gelled compositions, none of which are based upon the use of leather fibers as a thixotropic agent, include U.S. Pat. No. 3,417,018 Burns (use of mineral loughlinite), U.S. Pat. No. 3,714,041 Asgeirsson (colloidal silica in combination with particulate inorganic solids such as asbestos) and U.S. Pat. No. 2,887,461 Hort (use of a silica aerogel).
U.S. Pat. No. 4,350,723 Sugimura et al discloses peel-up type adhesives which comprise a rubber latex or resin emulsion which is film-forming and contains a fibrous material such as, e.g., collagen fibers obtained from the skins of beasts. Thickeners may be used but the thickeners do not include leather fibers. Further, the adhesives of Sugimura et al contain no volatile solvent, have a high inherent viscosity and in no fashion are suggested as being thixotropic.
U.S. Pat. No. 2,114,300 Gustin et al relates to molding compositions which include four basic ingredients: a filler, a gummy adhesive, Celluloid or a cellulose derivative and a drying oil or lubricant. The inert filler is disclosed as comprising leather fiber. When it is considered that it is mandatory to use a gummy adhesive in combination with Celluloid or a cellulose derivative, it is apparent that the compositions of Gustin et al could not be thixotropic in the sense of the present invention.
It has been known to use ground leather in drilling fluids in the prior art. See API BUL 13F, First Addition, August 1978. However, such ground leather is completely different from the leather fibers of the present invention.
Leather fibers have been used in making substitute leather products, reconstituted leather board, floor coverings and certain types of coating. Illustrative references dealing with the same include U.S. Pat. Nos. 1,302,810 Kirschbraum; 2,114,300 Gustin et al; 2,543,925 Monath; 2,601,671 Wilson et al; 2,643,234 Backus; 2,934,477 Highberger et al; 3,294,581 Hervey; 3,542,705 Mason et al; and 4,162,966 Parrini et al. None of these references disclose or suggest in any fashion that leather fibers could be used as a thixotropic agent.